1. Field of the Invention
The present invention relates to a process for the preparation of carboxylic acid esters which comprises reacting a carboxylic acid amide with a formic acid ester and/or an alcohol and carbon monoxide.
Carboxylic acid esters are commercially important substances, and as examples of the preparation of a carboxylic acid ester from a carboxylic acid amide, the preparation of acetic acid esters from acetamide, acrylic acid esters from acrylamide, metacrylic acid esters from methacrylamide, or .alpha.-hydroxyisobutyric acid esters from .alpha.-hydroxyisobutyramide may be cited. All these processes are commercially useful.
A preferred embodiment of the process of this invention is a process for preparing methyl methacrylate (hereinafter abbreviated as MMA) from .alpha.-hydroxyisobutyramide (hereinafter abbreviated as .alpha.HIBA) via methyl .alpha.-hydroxyisobutyrate (hereinafter abbreviated as M.alpha.HIB). This invention also relates to an industrial process for the preparation of MMA by the reaction mentioned above.
2. Description of the Prior Art
The process for the preparation of a carboxylic acid ester from a carboxylic acid amide which comprises decomposing a carboxylic acid amide with water and an alcohol in the presence of sulfuric acid is well known. However, this process has disadvantages that, for example, it gives rise to a large amount of ammonium sulfate by-product and it requires an expensive non-corrosive apparatus for the use of sulfuric acid.
In order to overcome these disadvantages, other processes which do not require the use of sulfuric acid are known for the preparation of carboxylic acid esters by the reaction between a carboxylic acid amide and an alcohol.
For example, Japanese Patent Disclosure No. 3015/1977 describes a process for the reaction of a carboxylic acid amide with a primary alcohol in the presence of a metal carboxylate which is at least partly soluble, and the carboxylate anion of which corresponds to the carboxylate residue of the desired ester. In Japanese Patent Disclosure No. 141216/1978, a process is described for the reaction of methacrylamide with a primary alcohol in the presence of a catalyst which consists of a combination of one or more species selected from copper, nickel, cobalt, and their compounds, and one or more compounds selected from a group consisting of compounds having at least one phenolic group, aldehyde group, ketone group, carboxylic acid group, amide group, or basic nitrogen containing group. In Japanese Patent Disclosure No. 144524/1978, a process is described for performing the reaction by the use of one or more catalysts selected from the group consisting of a bromide, fluoride, iodide, nitrate, phosphate, or borate of lead, cadmium, titanium, or tin.
However, all these processes cannot necessarily be regarded as commercially advantageous because they either suffers from the low activity of the catalysts, or they require an operation for the removal of ammonia from the reaction system intermittently or continuously during the reaction, in order to avoid the formation of a carboxylic acid amide and an alcohol by the reaction of a carboxylic acid ester and ammonia which are formed by the reaction.
Relative to the process for preparing MMA from .alpha.HIBA which is a preferred embodiment of the present invention, a typical process for the preparation of it known in the art is shown below.
MMA is prepared by the reaction of acetone cyanohydrin (hereinafter abbreviated as ACH) with methanol in the presence of concentrated sulfuric acid, said ACH being prepared by the reaction between hydrogen cyanide and acetone. However, this process is accompanied by the formation of a large amount of spent sulfuric acid and ammonium bisulfate by-products, and the hydrogen cyanide starting material is finally recovered as ammonium sulfate. Moreover, the quantity of ammonium sulfate which is produced, amounts to more than two tons per one ton of MMA, and this by-product formation has been a drawback of the process for the preparation of MMA by the ACH process.